The present invention relates to an extrusion apparatus and a method for extrusion.
Extrusion apparatus serve in the feed of material, especially plastics, whereby the extrusion apparatus is typically heated and the material that is fed in in granular or strip form is plasticized in the course of the extrusion process. In connection with the feeding in of material to be plasticized in strip form, it must be ensured that the extrusion worm is continuously supplied with sufficient material feedstock as otherwise an insufficient material feedstock leads inevitably to the inclusion of air which, depending upon the intended use of the respective extruded material, is not acceptable. In order to control the feeding in of the material feedstock, the material strip or granules are frequently fed from above to a horizontally extending worm. An example of this solution is disclosed in DE-OS 31 33 708. In this disclosed extrusion apparatus, the variations in the performance of the extrusion apparatus should be countered by a special storage zone of the extrusion worm.
A disadvantage of the noted solution is that a mixing occurs only on one side of a location, whereby in this respect the extrusion worm is radially loaded on one side. This condition can also result in a bending of the extrusion worm that, in turn, leads to a metal-on-metal rubbing of the side of the extrusion worm opposite to the radially loaded side, with the attendant disadvantages.
Research has shown that the quality of the feed is decisive for the performance of an extruder. Accordingly, efforts have been made to ensure the best possible synchronization between the feed rollers of the strip feed device and the drive of the extrusion worm. Nonetheless, there occurs in many instances involving a substantially radial feed a non-uniform degree of filling of the extrusion worm passage as a result of which it has been proposed to simultaneously fill several worm passages whenever possible. A solution of this manner is disclosed, for example, in DE-PS 40 05 400 in which it is endeavored to constantly maintain a blockage roll.
The just noted solution basically presents, in fact, an interesting approach. On the other hand, the material, before its actual plasticizing, is subjected to a decidedly strong shearing force that can be detrimental to the material properties.
The present invention accordingly provides a solution to the challenge of providing an extrusion apparatus that, in view of its total performance, is improved without necessitating especially burdensome measures with regard to controlling the feed of the material to be extruded.
In accordance with the present invention, the axial feed of material strips to the extruder permits the possibility of avoiding a one-sided radial pressure on the extrusion worm. Additionally, the extrusion worm is filled with feed material around its entire periphery, which provides the particular advantage of reducing the probability that air, which can degrade the quality of the extrudate, will be introduced in this area of the extrusion process.
The material strips can be fed at an angle onto the shaft between the drive motor and the extrusion worm and can be engaged by the shaft for drawing along by the shaft. In this regard, it is sufficient if the material strips are disposed at an angle in a hanging manner toward the shaft such that the engagement or take-up element of the shaft can, at the least, engage the material strips by frictional engagement.
In connection with this solution of the present invention, attention must be paid that a continuous feed to the extrusion worm is ensured. If the engagement or take-up element of the shaft is configured, for example, with a type of hook, the material strips can be manually hooked on at their leading ends. Thereafter, the engagement or take-up element in the form of hooks automatically draw the material strips at the proper speed and, thus, the corresponding proper feed volume for the extrusion worm and this is demonstrated in that the material fully encircles the extrusion worm in the transition areaxe2x80x94namely, the beginning of the extrusion worm. A particular advantage is realized in this connection in that the necessity of a partial back or counter flow, which brings with it the associated problem of shear loading of the material, can be completely avoided. The uniformity that is sought by use of a blockage roll automatically results in that a uniform condition of the feed material exists around the entire periphery of the extrusion worm.
In an advantageous embodiment of the present invention, it is provided that the material strips, instead of being wound in a plurality of windings about the shaft, are fed to the shaft in the manner of a pipe made of a continuous winding which has been axially extended out of its wound shape. This solution is particularly advantageous if a winding socket is rotated counter to the rotation of the extrusion worm and thereby ensures the required uniformity of the fed in material. In this solution, the material strips extend in the area of the shaft over approximately three-fourths of the circumference of the shaft, whereupon the desired distribution of the material is accomplished via the rotation and the counter-rotation.
It is particularly advantageous if the improved chamber filling of the extrusion worm leads to an improvement of about one-fifth in the output.
In accordance with a particularly advantageous embodiment of the present invention, it is provided that the transition area is configured between the shaft and the extrusion worm at the front end of the extruder housing and that the extruder housing at this location is configured with a widening or enlargement such that, as viewed in the direction of flow of the material, the transition area reduces or tapers conically. In this solution, a material strip hanging down to the shaft at an angle is simultaneously automatically engaged by the shaft and worked by the extrusion worm.
It is to be understood that the angle at which the material is fed into the feed zone can be selected to satisfy a wide range of requirements. For example, the material strips feeder, which comprises suitable feed rollers for the material strips, can be configured such that the angle of its output axis is oriented at an angle, for example, of 30xc2x0 relative to the shaft, whereby the intersection point between the output axis and the shaft is thus desirably immediately behind the beginning of the shaftxe2x80x94namely, adjacent the drive motor. The material strips are then directionally re-oriented upon engagement by the shaft and, in fact, re-oriented into an axis parallel direction such that the material extends parallel to the axis of the shaft upon reaching the transition area.
Further advantages, details, and features are set forth in the following description of one exemplary embodiment of the present invention together with the one FIGURE of the drawing.